Someone who gets drunk off a small amount of alcohol. Comes from Cadbury chocolate which is famous for having a glass and a half of milk in it. 'Cadbury's' only need a glass and a half (or similarly small quantity) to get drunk.

Jane is such a cadbury. She was drunk after her 2 glasses of wine last night.

1. A manufacturer of chocolates. Their famous slogan is that each of their blocks of chocolate contains 'a glass and a half of millk.'
2. A person who is easily affected by alcohol. This is based on the Cadbury 'glass and a half' slogan (ie: it only takes this person a glass and a half to get drunk!)

1. "I just had some Cadbury chocolate. Nice stuff'
2. "Haha, that girl is such a cadbury."

The etymology (ooooh, I know big words :-D) of this word starts with the need to avoid the use of the word 'Rack' (so as to alert a friend to a lovely set of bazookas WITHOUT the target being alerted). Thus (-> = becomes):-